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.\" $FreeBSD: src/lib/libc/gen/getcontext.3,v 1.3 2004/12/03 14:10:04 rse Exp $
.\"
.Dd September 10, 2002
.Dt GETCONTEXT 3
.Os
.Sh NAME
.Nm getcontext , setcontext
.Nd get and set user thread context
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In ucontext.h
.Ft int
.Fn getcontext "ucontext_t *ucp"
.Ft int
.Fn setcontext "const ucontext_t *ucp"
.Sh DESCRIPTION
The
.Fn getcontext
function
saves the current thread's execution context in the structure pointed to by
.Fa ucp .
This saved context may then later be restored by calling
.Fn setcontext .
.Pp
The
.Fn setcontext
function
makes a previously saved thread context the current thread context, i.e.,
the current context is lost and
.Fn setcontext
does not return.
Instead, execution continues in the context specified by
.Fa ucp ,
which must have been previously initialized by a call to
.Fn getcontext ,
.Xr makecontext 3 ,
or by being passed as an argument to a signal handler (see
.Xr sigaction 2 ) .
.Pp
If
.Fa ucp
was initialized by
.Fn getcontext ,
then execution continues as if the original
.Fn getcontext
call had just returned (again).
.Pp
If
.Fa ucp
was initialized by
.Xr makecontext 3 ,
execution continues with the invocation of the function specified to
.Xr makecontext 3 .
When that function returns,
.Fa "ucp->uc_link"
determines what happens next:
if
.Fa "ucp->uc_link"
is
.Dv NULL ,
the process exits;
otherwise,
.Fn setcontext "ucp->uc_link"
is implicitly invoked.
.Pp
If
.Fa ucp
was initialized by the invocation of a signal handler, execution continues
at the point the thread was interrupted by the signal.
.Sh RETURN VALUES
If successful,
.Fn getcontext
returns zero and
.Fn setcontext
does not return; otherwise \-1 is returned.
.Sh ERRORS
No errors are defined for
.Fn getcontext
or
.Fn setcontext .
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr makecontext 3 ,
.Xr ucontext 3